Yes you can go to Ollivanders as many times as you want, but you need to fill out the wand quiz and RP getting your wand each and every time. However, it would mean your character doesn't have a wand anymore for whatever reason, maybe because it broke so keep that in mind. It wouldn't be appropriate to do it more than once a term though and most witches and wizards would be very careful with their wands, so they wouldn't often need replacing.

If you just want a different wand, you can simply make one up and add it to your profile.